Vacuum tube with tank circuits



.Aug. 3, 1937. R. POTTER VACUUM TUBE WITH TANK CIRCUITS Filed June 12, I936 25 Sheets-Sheet l INVENTOR Z-Kfiotler 2 m B 2 I d 2 12 A I M ATTORNEY Aug. 3, 1937. R. K. POTTER VACUUM TUBE WITH TANK CIRCUITS Filed June 12, 1936 5 Sheets-Sheet 2 z; 4 c, 0 c6 b LL Z c a 0' g [a F i f r f w W Z c a a 2' INVENTOR 50 i. (0 4m BKPOZLLZV ATTOR NEY Aug. 3, 1937. R. K. POTTER VACUUM TUBE WITH TANK CIRCUITS Filed Jun'e 12. 1.936

5 Sheets-Sheet 5 CoI wizwtive SizeZZ Plate,

Iv T x 06 0 ooooauoeoaooocooovu e m M a INVENTOR 15306 tel/- fw fi 'I ATTORNEY Patented Aug. 3, 1937 UNITED STATES 2,088,722 VACUUM TUBE WITH TANK CIRCUITS Ralph Kimball Potter,

Madison, N. J., assignor to American Telephone and Telegraph Company, a corporation of New York Application June 12,

8 Claims.

This invention relates to radio frequency oscillation generators and more particularly to generators of very high frequencies such as are used in so-called short-wave signaling.

mon subject matter of my United States application Serial No. 746,902, filed October 4, 1934.

Its purpose is to design an arrangement in which very high frequencies of great stability 10 are obtained and in such manner that the oscillations shall be relatively free from disturbances outside its own circuit and shall produce a. minimum of disturbances on or in adjacent surroundings. Its purpose is also that of providing an oscillatory circuit for a generator of very low damping factor.

To accomplish these purposes I make use of certain forms of impedances, described in my Patent No. 2,030,178 issued February 11, 1936. In

that patent I describe a typejof impedance which may be called a tank impedance" and which, in one form, may consist essentially of a cylindrical conductor with both ends closed orvnearly closed. One simple form which. thetanb with a line circuit may take is that" of two *relatively small concentric conductors constituting the line over one end of which is placed a large concentric conductor with the one end closed by a disk to the inner of the pair of conductors and the other end closed by a diskto the outer of the pair of conductors. As pointed out in my said application, such a circuitjacts as a small but concentrated or lumped inductance'at the one end of the pair of conductors and equations are given for the approximate magnitude of the inductance in any given case. It is also pointed out how lumped capacity may be introduced in such a device, leading to resonant and anti-resonant circuits. In this invention I show some applica- 40 tions of such circuits to oscillation generators and to tuned amplifiers both in a manner to yield low damping in the oscillatory circuits and to yield a generator or amplifier which is especially well shielded from extraneous disturbances which become so serious at the high frequencies here contemplated.

The invention will be better understood by reference tothe following specification and the accompanying drawings, in which Figures 1a to 1d illustrate the type of inductances and tuned circuits which I propose to use; Figs. 2a and 2c show the connection of such an inductance into a certain type of circuit and Fig. 2b shows the equivalent more conventional appearance of that circuit; Figs. 3a to 8b show a series of circuits This application is a continuation as to com-v 1936, Serial No. 84,968

in pairs, the one giving the circuit with my new form of inductance and the other the equivalent circuit in more conventional form; and Figs. 9a to show important modifications of my circuit in which the amplifier elements necessary for the generator or amplifier are included within the tank.

In the conventional oscillatory circuit the magnetic and electric fields exist outside as well as inside the coils and condensers of those circuits. In the case of most inductance coils the external 7 field may be quite extensive but also may be very materially reduced by having it take the well known form of a toroid. At very high frequencies where radiation from oscillatory circuits and spurious coupling effects are of more than usual importance, the characteristics of the toroid coil are desirable. At extremely high frequencies, however, the inductance and capacities required become small and also the skin eifect increases in such manner that large conductors are needed in order to provide low loss circuits. The inductance itself may then reduce to a single turn of heavy conductor, as illustrated in Fig. la, but in this case the magnetic field is widely distributed. To confine the field to a small region, I have found it is necessary, as pointed out in my copendingapplication, to make this single turn the equivalent of a coil, the surface of which is reentrant in the same way as in toroidal coils, and the single turn coil in this reentrant form becomes Qthen what may be called a tank because of its physical appearance.

The term tank" or tank circuit as used in this specification and the claims, is defined as an enclosing conducting vessel of one or more compartments, enclosing various associated elements, and in which the inner surface of the vessel constitutes an essential part of the path for high frequency currents. Such a tank circuit with capacity included to form a resonant circuit is shown in Fig. 1b and may be looked upon as a figure of revolution, obtained by rotating the circult of Fig. 1a about the line b-b as an axis although not shown to scale, particularly as respects flanges a and d. If the circuit, of Fig. la had been circular instead of rectangular and a similar rotation had occurred, a tank of the form shown in Fig. 10 would have resulted, possessing the same electrical properties as Fig. lb. Here, however, a portion of the fiange extending toward the center of Fig. 1c is omitted for structural simplicity, the electrical effect of the omission being negligible. In these two cases'the capacity of the circuit is included within the tank and is effectively shielded so far as external objectsare concerned. A somewhat different form of tank,

but substantially equivalent, is shown in Fig. 1d,

obtained by rotating the circuit of Fig. 10. about the line M as an axis, and in this case the condenser is on the external edge of the tank. These, as well as many other forms which the tank circuits may take, are described in my copending application mentioned above.

In Fig. 2a there is shown a tank circuit replacing the conventional arrangement of coils and condensers. Thus the lead I, which may be an antenna or any other output is shown connected to ground through the resonant circuit consisting of inductance and capacity. again, as in Fig. 1c, the shape of the flanges is slightly modified, one of the extensions being omitted and the other being connected completely across the center for greater convenience in connecting the antenna. The conventional form of circuit which is equivalent is shown in Fig. 2b. In Fig. 2a it should be emphasized that, at the frequencies contemplated, the currents are surface effects only and cannot pass through the body of the metal. Thus, in this case one path to ground is across the condenser a-d and the other is around the inductive path ar-bc-d inside the tank, that is, the circuit comprises a condenser and inductance in parallel as in Fig. 2b. It will be recognized that the high frequency magnetic field due to the current flowing on the outer surface of the inner cylinder of the tank cannot penetrate through the outer boundary of the tank, and thus the magnetic field due to current on the inner conductor is confined within the tank. Furthermore, it will be recognized that any of the high frequency currents flowing on the inner side of the outer cylinder will produce no magnetic field within the tank. Also high frequency currents flowing on the outer surface of the outer cylinder, will produce no magnetic field within the tank. Thus there is no coupling between the inside of the tank and the outside of the tank through the walls of the tank. The outside of the tank may be considered the ground in the same way that a metal shield around a circuit is ordinarily taken as ground. To visualize the conditions more clearly, the tank might actually be buried in the ground, as shown in Fig. 2c. The impedance to ground at resonance is determined by the resonant circuit constants similarly in all three cases. The tank circuit here shown is of the type illustrated by Fig. 6a in my copending application.

Fig. 3a shows the use of the tank circuit in a vacuum tube oscillation generator, this being equivalent to the circuit of Fig. 3b, which in turn is a well known generator, frequently spoken of as the ultraudion oscillator.

Fig. 4a shows another circuit including my tank circuit and which is the equivalent of the circuit of Fig. 4b, this being an oscillator generator commonly spoken of as the dynatron oscillator."

In Fig. 5a I show a generator with two of my tanks, the circuit being the equivalent of that shown in Fig. 5b, sometimes called the tuned grid tuned plate oscillator." It will be observed that each of the oscillator circuits of Fig. 5b has been replaced by tanks.

Figs. 6a and 6b are a pair of equivalent circuits and are the familiar Colpitts oscillators." The conventional oscillatory circuit comprising 15 condensers Cl, C: and inductance L, is replaced by a tank of the form illustrated by Fig. 13 or 19 of my copending application. In this tank the plates 0, d and b make the condensers C1 and C: of Fig. 6b. Potential variations coming from the plate of the tube give rise to currents across the condensers in series and, in parallel to these condensers, through the inductance of the tank in a manner analogous to the circuit of Fig. 6b. In order to illustrate how a load may be connected to this circuit, there is shown an antenna connected to the plate b and earth connected to the plate d, this corresponding to an antenna and earth connected in parallel to the condenser C2 of Fig. 6b, with the midpoint or filament connected to earth;

Figs. 7a and 7b also show a pair of equivalent circuits, the circuit of Fig. 7b being that commonly known in the art as the Hartley oscillator. Here the conventional, oscillatory circuit, comprising inductances L1, L2 and ondenser C, is replaced by a tank. The connectisrgin the Hartley circuit from the filament to the int between the two inductances finds its equivalence in Fig. 7a by the connection to the midpoint of the tank inductance at M, and it is evident that this may be made adjustable to vary the ratio of the inductances L1 and L2. Such a connection may consist of a single radial conductor but for better current distribution may consist of several radial conductors or even a partition with a number of apertures which would determine the coupling between the two inductances. This connection is obviously similar to the usual connection to some midpoint of a single turn inductance coil.

Figs. 8a and 8b represent the so-called Meissner oscillator", in which the resonant circuit, consisting of inductance L and capacity C, is replaced by my tank circuit. The method of coupling L and L" to L is clearly shown in Fig. 8a and is equivalent to the usual method of coupling to a solenoidinductance. The loops L and L" of Fig. 8a are arranged to include a suflicient amount of the magnitude flux within the tank inductance L to provide the required coupling.

One of the marked advantages of the circuits which have just been described is the comparative freedom from electric or magnetic coupling with external circuits and conducting bodies. An important part of my invention consists incarrying this shielding effect to an even greater extent by enclosing the vacuum tube amplifier within the tank itself so that all parts of the circuit are within the tank, with the possible exception of the batteries, to which connection can be made by short leads through the walls of the tank. Such arrangements are shown in Figs. 9a, 10a and 11a.

The arrangement shown in Fig. 9a is similar to that of Fig. 7a; that is to say, it is a Hartley type of oscillator circuit, but in Fig. 9a all of the parts, excepting the batteries, are placed within the tank circuit. In Fig. 9a. the axis of the tank may be looked upon as a vertical axis through the center of the tank. In general this tank will be of ample capacity to accommodate the vacuum tube and accompanying elements with suitable supports. As will be clear from the drawings, the vacuum tube VT with its filament, grid and plate, is mounted in the tank as shown and the condenser C leading from the grid to one terminal of the inductance formed by the tank, the resistance R connected between the grid and the filament, and the capacity C. in the connection from the filament to the midpoint of the surface of the tank, may all be suitably mounted within the tank itself. Connections will extend out through an opening in the bottom of the tank to the batteries for supplying the filament and plate currents. The grid potential is, of course, derived through the drop of the resistance R. The flanges near the center of the tank provide the main capacity C of the oscillator.

Fig. 9b shows an equivalent circuit employing l conventional types of electrical elements. In Fig.

9b the main capacity C of the Hartley circuit corresponds to the capacity of the flanges in the center of the tank, and the two inductances L1 and L3 are the inductances formed by the interior 15 surface of the tank, from the midpoint along the inner surface of the wall to the upper flange on the one hand, and over the inner surface of the wall of the lower half of the tank to the lower flange on the other hand. The high frequency currents flowing over the inner surface of the tank will not be propagated out of the tank along the batteryconnections because the oscillatory currents are propagated over the interior surface of the tank and flow around the opening, instead 25 of across it, to the load circuit.

Fig. 10a shows an oscillator of the Colpitts type and is essentially the same in principle as the circuits of Figs. 6a and 6b. In Fig. 10a the axis of the tank is longitudinal instead of vertical as 30 in Fig. 1b. The outlet tubes of the tank are of smaller diameter and the capacity forming flanges are omitted, capacities being formed, however, between the inner surfaces of the outlet tubes and the outlet wires as shown at C and Co. In Figure a the vacuum tube is shown at VT within the tank and the two main tuning capacities C1 and C2 of the Colpitts type circuit are likewise mounted within the tank and are connected at their common point to the filament F, with their other terminals connected to the conductive outlet tubes through which external connections are made. These outlet tubes are also connected through capacities C5 and C4 to the grid G and plate P, respectively, of the vacuum tube. The capacities C3 and C4 will also be mounted within the tank. The grid potential is supplied from a battery which has one terminal connected to the outer surface of the tank (which may be grounded, if desired), the other terminal of the battery being connected to a conductor leading concentrically through the cylindrical outlet tube to the grid. There will be, of course, some capacity at C5 between this conductor and the inner wall of the cylindrical outlet tube.

Likewise the plate battery has one terminal connected to the outer surface of the tank and the other terminal is connected through a choke coil L4 to a conductor passing concentrically through the cylindrical outlet tube to the plate. A ca- G0 pacity C5 will exist between the conductor and the outlet tube. If the capacities C5 and Co are sufiiciently large, the separate capacities C3 and 04 may be omitted. The two conductors from the filament are connected through a double 65 wound choke coil L3, the one to the inner wall of the tank and the other through an opening in the wall of the tank to the filament battery, the other terminal of which is connected to the outer wall of the tank. The currents flowing over the inner 70 walls of the tank from the terminals of the choke L3 to the capacities'C5 and Cs are subjected to the inductance effect of the walls of the tank. The equivalent circuit is shown in Fig. 10b. As

is well understood the Colpitts type circuit has 75 two capacities C1 and C: with their common terminal connected to the filament and with their opposite terminals connected to the grid and plate as shown in Fig. 10b, and with a single inductance connected from grid to plate in parallel to the two condensers. In Fig. 10b as shown, the single inductance is divided into two parts L and L" which, from the high frequency alternating current standpoint, function as a single inductance. A midtap is provided, however, for the necessary connection to permit the battery current to be supplied to the filament. The inner surface of the tank walls provides an inductance (corresponding to L' and L" in Fig. 10b) whose midpoint, the junction of L and L", is connected to the filament through L3, the other terminals of the inductance being connected to the capacities C1 and C: by the connection of said capacities to the outlet tubes of the tank. Unlike the tank circuit of Fig. 3a, the main tuning capacity or capacities (C1 and C2) are not part of the tank circuit of Fig. 10a. The choke coil In prevents alternating current from entering into the filament leads. From an alternating current standpoint, therefore, the circuit is a true Colpitts circuit, as the two elements L and L" function as a single inductance without high frequency connection to the filament. It will be clear from Fig. 10b that the capacities C5 and C5 which exist between the outlet conductors and the tubular cylindrical outlets through the walls of the tank are effectively in parallel to the capacities C3 and C4.

In Fig. 11a the tank has a horizontal axis and the circuit is essentially that of a Hartley oscillator. The filament is connected to the midpoint of the inner surface of the tank by having one of the filament leads connected to the wall of a cylindrical outlet tube through the side wall of the tank, the other filament connection passing concentrically through this outlet tube to the battery, the other terminal of which is connected to the outer wall of the tank. Thus from an alternating current standpoint the inner surface of the tank is divided into two paths for the flow of current-from the filament to the grid on one hand and from the filament to the plate on the other, thus forming the two inductances L1 and L2 of the Hartley type oscillator as shown in Fig. 11b. The main condenser C of the Hartley circuit has its terminals connected, respectively, to the outer surfaces of the cylindrical outlet tubes. As in Fig. 10a, capacities C3 and C4 are connected between the outer surfaces of the outlet tubes and the grid and plate, respectively. These two capacities and capacity C are mounted within the tank as in the vacuum tube VT itself. Capacities C5 and Cs effectively in parallel with the capacities C3 and C4 exist between the outlet conductors and the cylindrical outlet tubes, the electrical equivalent being shown in Fig. 11b. As in the case of Fig. 10a, capacities C3 and C4 may be omitted if capacities C5 and C5 are sufficiently large. The direct current potentials for the grid and plate are supplied in the same way as in Fig. 10a.

In the three arrangements shown in Figs. 9a, 10a and 11a, respectively, the output of the oscillator would be a radiating antenna or something equivalent thereto and, for illustrative purposes, antennae have been shown connected to the plate circuit of the tube VT in each of these figures. In Fig. 90, for example, the antenna is connected to the flat disc-like flange forming the lower plate of capacity C, and the current flows over this flange to the plate electrode of the tube VT. In Figs. 10a and 11a, on the other hand, the antenna 'is led in to the plate by a lead-in wire passing through the interior of the outlet tube of the tank.

This feature of enclosing the vacuum'tube and 5 certain auxiliary apparatus within the tank is suitable not only for oscillators but for amplifiersband'it may well bethat in any given case one could wish to redesign the vacuum tube in order to adapt it to the particular situation in hand. For example, the'vacuum tube might be redesigned so as to be built into and form a part of the tank structure'itseli.

If one were to use the tank and vacuum tube as an amplifier, then the essential elements would be those shown in Fig. 124 where the tank axis is horizontal. In this case a double tank of the kind illustrated in Fig. 16 of my copending application, Serial No. 746,902 is shown. For purposes of discussion the elements of a simple three-element vacuum tube are illustrated schematically by F, G and P, for filament, grid and plate, respectively. The capacities in resonant circuits are, for the purpose of argument, provided by the capacities between tube elements.

ing the capacity between F and G and the inductance a bc-d. In the output there isa resonant circuit with capacity between G and P and inductance a-b-c.'-d'. The equivalent of this circuit is shown in Fig. 1227 where the tube element capacities are C r, Cm. Depending upon the effectiveness of shielding provided by the grid G, or any other more complicated structure replacing this grid, there will be more or less capacity between F and P of Fig. 12a,; the equivalent in Fig. 12b is determined by the size of the hole in the partition .1: between plates 1! and 2. If the partition were solid the capacity coupling between 1! and 2 would be zero.

40 To make use of the circuit of Fig. 12a, as an amplifier for example, it is necessary to provide means to get into and out of the tank. A practical amplifier circuit arrangement is shown in Fig. 13a with an input at the left and an output at the right in the form of concentric conductor transmission lines. TLi and Th2. Here the three tube elements, filament F, grid G and plate P are surrounded by a glass envelope to provide tor the evacuation. The envelope may in turn be and is here shown as enclosed within a conductive shell which provides additional capacity shunting the inter-element capacities. The filament battery B1 is connected through the choke coil L: (with a winding in each filament lead) to conductors led in through the interior of a pipe forming the continuation of the central conductor of the concentric conductor transmission line TL1. From the inside of this pipe the filament leads pass through the glass walls of the vacuum tube 0 to the twoterminals of the filament F. The plate supply from battery B2 is also ledthrough a choke 001114 to the central conductor of the output line TLa, and to the plate of the tube as shown.

Capacities C: and C: are formed between the 5 two halves of the conductive shell with its flanges, and the mid-wall a: of the tank, and hence are in efiect connected to the grid G which is mounted in the mid-wall. This is shown in the equivalent circuit 0! Fig. 131) where capacities C: and C: are

7 connected from the grid to the central conductors of the transmission lines TLi and TIA, respectively. The capacity C: is in this manner connected directly to the plate but capacity C: is connected to the filament through the capacity '5 C: which exists btgeen the inner wall 0! the In the input there is a resonant circuit contain-.

inner concentric tube and the filament leads. A capacity Ci exists between the innersuriace oi the concentric conductor and the inner conductor oi the transmission line TLi. A similar capacity C4 exists between the inner and outer conductors of the concentric transmission line 'I'La. High frequencies will not pass from the interior of said transmission line over the plate battery connection because of the choke coil L4 and because the high frequencies find a low impedance path around the opening in the wall.

The equivalent circuit shown in Fig. 13b illustrates the relative arrangements of the various capacities, inductances and other elements of the circuit. The inductances L1 and L: are formed by the separate inner surfaces of the two compartments of the tank. It will be seen that a high frequency tuned circuit exists between filament F and grid G and between plate P and grid G. The former may be traced from the filament F, through the capacity Cr, through the capacity Cl and the inductance L1 to the grid, a parallel path extending from the capacity C1 through the capacity C: to the grid. Likewise the plate-grid circuit may be traced from the plate P through the capacity C4 in series with the inductance L2 to the grid, this capacity and inductance being shunted by the capacity C;.

The essential elements of the circuit oi Fig. 130. are shown in simplified form in Fig. 130 and it will be noted that the input and output circuits are capacity coupled to the resonant tank circuits, since the capacities C1 and C4 of Fig. 13b are across the transmission lines Th1 and I10 and form with capacity C: and C3, respectively,

the total tuning capacities included in each of the circuits.

A signal input from the transmission line TL; of Fig. 130 sets up oscillations within the associated tank circuit and produces a resonant voltage between F and G. The steady flow of electrons between F and P provided by the d -c field between these elements is, accordingly, modulated in the well known manner, and the field between G and F is varied in such a way as to set up am-' plified oscillations in the second circuit similar to those impressed in the first. It is, of course, necessary to adjust these circuits to provide reso nance as in any conventional amplifier of this type. This may be accomplished by varying the positions of the two conductive shells S1 and S2, or by any design of the structure which will permit equivalent variations. For example, we might make the length oi. one of the tank circuits adjustable, as indicated, by the sliding contact to the conductor TL1. I

The vacuum tubes used in Fig. 13a may be physically modified forms of any of a variety of tubes, either three-element or four-element tubes, or others, which are suitable for amplifiers or oscillation generators. The elements may be concentrically arranged as shown in Fig. 14a

where the grid and plate elements of the vacuum tube are in cylindrical form about a common axis with the filament located in said axis. Again the cathode, grid and plate may be related to each other in the manner indicated in Fig. 14b. In the latter, a heater, a cathode, a grid and a plate element are shown with the grid placed between cathode and plate and forming a continuous mesh disc with a mesh or solid edge that is brought outside of the whole periphery of the vacuum tube. When this vacuum tube is set into an aperture of the partition 1: of Fig. 120 or Fig. 134 and contact is made all the way around by a clamp or other mechanical means, the coupling between the two tank circuits is restricted to that through the grid which functions as a control element. If it should be desirable to apply a d-c 6 bias to the grid the above mentioned contact may be broken by a spacer of some insulating material which would provide a low impedance path for the high-frequency currents while isolating the d-c potential.

To make the amplifier arrangement of Fig. 13a function as an oscillator, it is necessary to provide coupling of suitable magnitude and phase between the oscillation in the first and second tank circuits. Such coupling may be provided in a number of ways and, in particular, may be provided by apertures in the partition .1. Such apertures are shown at a and a in Fig. 15c which, it will be noted, is similar to Fig. 12a in the showing of a few essential elements. The coupling between the two tank circuits will be dependent, among other things, upon the total area of the apertures.

In Fig. 15a. there is shown schematically an oscillator arrangement in which an aperture coupling between tank circuits, of the type just described, is used. There is also shown a capacity which isolates the grid. The coupling aperture is provided in the mid-wall a: which, in this case, is connected directly to one-half of the conductive shell. The grid is then mounted in another conductive plate between which and the mid-wall a: of the tank (a part of which is formed by one-half of the conductive shell) a capacity Ca exists. This capacity isolates the grid from themid-wall of the tank. A similar capacity C: exists between the plate in which the grid is mounted and the other half'of the conductive shell with its flanges, thereby isolating the grid from any connection to the walls of the tank 40 through the tubular conductor which permits of the battery connections to the heater H. The capacity C2 also isolates the grid from the cathode F.

The aperture coupling is in reality an induc- 45 tive coupling since it permits current in one chamber to fiow into the other and this forms a conductor (or inductance) common to the two circuits. The effect. of this will be clear from the equivalent circuit'shown in Fig; '15!) where 50 L1 and In representth'e inductances due .to the current flowing over the inner surfaces of the two compartments of the tank, while M represents the inductive coupling between the .two parts of the tank due to the current flowing". from 55 one compartment of the tank to the other through the aperture.

In addition to the coupling due to the aperture in'th'e partitionwalhthere may-beanother-kindof coupling betweenv the two'compartments. For 60 example, an opening in the partition running all the way around the vacuum tube, as illustrated by the grid isolating capacity" previously mentioned, forms a capacity common to the input and output circuits. 5 the grid is not only isolated by the capacity C3, as just stated, butit is also isolated from another standpoint by the capacity C: between the conductive shell and the mounting of the grid.

The effect of these capacities is shown in the 7 equivalent circuit of Fig. 151?. Here it will be seen that the grid circuit and the plate circuit are coupled not only by the mutual inductance M but by the capacity C3. It will be evident that the magnitude of the coupling depends upon the 7 size of the aperture or isolating capacity. The

- in the other chamber.

As previously mentioned,

phase of the feed-back from one tank circuit to the other, depends upon the relative size of these two coupling elements as in any conventional circuit. This provides means for adjusting the phase of the feed-back as is required.

While the figures have thus far been described with the implication that they are right circular cylinders, it is to be understood that no such restriction is necessary. The enclosing vessel might, for example, be a cube or other parallelopiped with the main entrances to the vessel at the centers of two opposite faces or at two opposite corners. Again the vessel may take on the form of a sphere with the chief entrance points at the ends of a diameter. In any of these cases the magnetic field set up within the vessel would probably be somewhat more distorted than in the case of a circular cylinder, but each vessel would have a definite inductance. It is not even necessary that the entrance p'oints shall be symmetrically arranged as indicated above, but they might be at any two points on the vessel, although in that event the distortion in the magnetic field would be greater and the lack of symmetrical distribution of the surface currents would tend to make the losses somewhat larger.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit of the invention as defined in the following claims.

What is claimed is:

1. In an amplifier circuit, an amplifier tube having electrodes, a plurality of inductances and capacities connected with stantially closed conducting vessel constituting said electrodes, a subwith enclosed elements a tank circuit, a conducting partition within said tank forming two chambers, connections from said electrodes to the inner surfaces of said chambers enabling current to flow over the inner surface of each chamber, the inner surface of each chamber thereby constituting one of said inductances.

2. In an amplifier circuit, an amplifier tube having cathode, anode and control electrodes, a plurality of inductances and capacities connected with said'electrodes, a substantially closed .conducting vessel constituting with enclosed elements a tank circuit, a conducting partition within said tank forming two chambers, connections from said-electrodes to the inner surfaces of said chambers enabling current to flow over the inner surface of each chamber, the inner surface of each chamberthereby constituting one of said inv ductances, the structure of the amplifier tube being mounted within the tank with the cathode electrode; in one chamber and the anode electrode 3. In an amplifier circuit, an amplifier tube having cathode, anode and control electrodes, a plurality of inductances and capacities connected with said electrode, a substantially closed conducting vessel constituting with enclosed elements a tank circuit. a conducting partition within said tank forming two chambers, connections from said electrodes to the inner surfaces of said chambers enabling current to fiow over the inner surface of each chamber, the inner surface of each chamber thereby constituting one of said inductances, the structure of the amplifier tube being mounted within the tank with the cathode electrode in one chamber, the anode electrode in the other chamber and the control electrode in the plane of the partition.

4. In an oscillation generator, a vacuum tube having cathode, anode and control electrodes, a plurality of inductances and capacities connected with said electrodes, a substantially closed conducting vessel constituting with enclosed elements a tank circuit, a conducting partition within said tank forming two chambers, connections from said electrodes to the inner surfaces of said chambers enabling current to flow over the inner surface of each chamber, the inner surface of each chamber thereby constituting one of said inductances, the vacuum tube structure being mounted within the tank with the cathode electrode in one chamber, the anode electrode in the other chamber and the control electrode common to both chambers, and apertures in the partition for producing an inductive coupling between the input and output circuits of the tube.

5. In an oscillation generator, a vacuum tube having cathode, anode and control electrodes, a plurality of inductances and capacities connected with said electrodes, a substantially closed conducting vessel constituting with enclosed elements 9. tanlmcircuit, a conducting partition within said tank forming two chambers, connections from said electrodes to the inner surfaces of said chambers enabling current to flow over the inner surface of each chamber, the inner surface of each chamber thereby constituting one of said inductances, the vacuum tube structure being mounted within the tank with the cathode electrode in-one chamber, the anode electrode in the other chamber and the control electrode common 'to both chambers, apertures in the partition 'for producing an inductive coupling between the input and output circuits of the tube, said tank structure having elements so formed as to produce with adjacent surfaces capacities for tuning the input and output circuits of the tube.

6., In a vacuum tube circuit, an amplifier tube having an input circuit and an output circuit, a substantially closed conducting vessel enclosing said tube and constituting a tank whose inner surface acts as an inductance with respect to currents flowing over it, a conducting partition within said tank forming two chambers, the one chamber being connected with the input circuit so that current flows over its inner surface and causes it to function as an inductance in the input circuit, and the other chamber being connected with the output circuit so that current fiows over its inner surface and causes it to function as an inductance in the output circuit.

7. In an amplifier circuit an amplifier tube having cathode, anode and control electrodes, an input circuit connected with said cathode and an output circuit connected with said anode,-a substantially closed conducting vessel enclosing said tube and constituting a tankwhose inner surface acts as an inductance with respect to high-frequency currents flowing over it, a conducting partition within said tank forming two chambers, each chamber constituting an inductance, the vacuum tube being so mounted in the tank that its cathode electrode is in one chamber and its anode electrode in the other chamber, the one chamber being connected with the input circuit connected with the cathode electrode so that current flows over its inner surface and causes it to function as an inductance in the output circuit, and the other chamber being connected with the output circuit connected with the anode electrode so that current flows over its inner surface and causes it to function" as. an inductance in the output circuit.

8. In an amplifier circuit, an amplifier tube having cathode, anode and control electrodes, an input circuit connected with said cathode and an output circuit connected with said anode, a substantially closed conducting vessel enclosing said tube and constituting a tank whose inner surface acts as an inductance with respect to high frequency currents flowing over it, a conducting partition within said tank forming two chambers, each chamber constituting an inductance, the vacuum tube being so mounted in the tank that its cathode electrode is in one chamber and its anode electrode in the other chamber, the one chamber being connected with the input circuit connected with the cathode electrode so that current flows over its inner surface and causes it to function as an inductance in the input circuit, and the other chamber being connected with the output circuit connected with the anode electrode so that current flows over its inner surface and causes it to function as an inductance in the output circuit, and elements within said tank to produce capacities with certain of the surfaces of said tank, one of said capacities being included in" the input circuit and another of said capacities being included in the output circuit.

RALPH KIMBALL POTTER- 

